Coherent manipulation, measurement and entanglement of individual solid-state spins using optical fields

Abstract

D ue to their insensitivity to electrical noise, spin degrees of freedom are widely considered to be promising candidates for storing information 1-3 . To operate a confined spin as a memory element for quantum information, it is essential to fully controllably turn on and off its coupling to external charge or electromagnetic degrees of freedom so that quantum information can be reliably written or read out. The spin-orbit interaction plays a crucial role in this endeavour, either by providing means for direct electrical manipulation of spins or by enabling spin-dependent optical transitions where different spin-states couple to light fields with different polarization or frequency (Box 1). Of particular interest is the realization of a spin-photon quantum interface 4-7 . In this Review, we primarily focus on recent advances that use quantum entanglement between a confined spin and a propagating photon to demonstrate basic quantum information protocols between distant qubits 8-10 .To generate a spin-photon quantum interface, spin-orbit interaction is only required to be strong in the optically excited state. As thermal excitation to the optically excited states is completely negligible, the spin remains isolated from its environment unless a laser field is applied. It should be emphasized that incoherent optical manipulation of spin ensembles is not new and has been extensively used by physicists and chemists alike in optical pumping, dynamical nuclear spin polarization and Kerr rotation experiments since the 1950s. More recently, motivated by potential applications in quantum information processing, a promising research direction investigating quantum coherent optical manipulation and measurement of individual isolated spin qubits has emerged. When the individual spins are embedded in a solid-state matrix, nanofabrication techniques enable the integration and control of qubits on chips, potentially paving the way for a scalable quantum information processing architecture 2,11-13 .Although various promising approaches to scalable quantum computation are being actively pursued, quantum communication research has been exclusively based on the use of single-photons as flying qubits carrying quantum information over long distances. For this application, the availability of a quantum interface between Realization of a quantum interface between stationary and flying qubits is a requirement for long-distance quantum communication and distributed quantum computation. The prospects for integrating many qubits on a single chip render solid-state spins promising candidates for stationary qubits. Certain solid-state systems, including quantum dots and nitrogen-vacancy centres in diamond, exhibit spin-state-dependent optical transitions, allowing for fast initialization, manipulation and measurement of the spins using laser excitation. Recent progress has brought spin photonics research in these materials into the quantum realm, allowing the demonstration of spin-photon entanglement, which in turn has enabled distant spin en...

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